1. Field of the Invention
The present invention relates to an injection-molded body provided with undercuts.
2. Description of the Related Art
Presently, injection-molded bodies of a variety of shapes are formed for a variety of applications by a variety of injection molding methods. In the auto industry and other fields of industries, a variety of parts are formed by injection molding. For example, there is a variable resistor used in a rotation angle detecting sensor (hereinafter, referred to as the “valve sensor” where appropriate) of a swirl control valve used to generate a longitudinal or transverse vortex of air by being opened or closed when a mixture of gasoline and air is fed into a cylinder on an air intake side of an engine. In such a variable resistor, a housing including a rotor of the variable resistor is formed by injection molding.
Since the above-described housing of the valve sensor as the injection-molded body is assembled into a portion in which air intake is controlled, the housing needs a sufficient airtightness. For this reason, seal members such as O-rings are provided where necessary, and so-called undercuts for preventing those seal members from falling off are provided in the housing. Presently, undercuts of such injection-molded bodies are formed by using parts such as slide cores or in processes such as forced demolding (for example, see Japanese Unexamined Patent Application Publication No. 2001-300971).